Is this an overheating computer problem?

The vast majority of the time, my computer is as close to 100% problem-free as it’s possible for a Windows machine to be. However, when I try to convert large video files from one format to another (usually using the registered version of WinAvi Converter), the computer will spontaneously shut itself down and restart after working for about 10 minutes or so on the conversion. My machine is a couple-three years old and it does use 100% of the cpu to convert big files. I’ve already done the most basic fix, opening the case and blowing all the dust out, but the problem persists.
Ideas? Fixes?

Download a free copy of Speedfan, you can watch a graph of your temps while you are converting video.

Okay, I did that and the temperature does climb pretty quickly during converting. Now, what are the possible fixes?

How many fans does your system have? Is your system inside of a desk? Is there adequate ventilation? You could try pulling the side off, and see how the temps behave. If that improves the operation, consider adding another case fan, if you have space for it. You could also pull the heat sink off and add a smear of thermal grease to insure good contact between your CPU and the heat sink.

Thanks. I’ll try it.